The use of nucleic acid sequences to vaccinate against animal and human diseases has been studied. Studies have focused on effective and efficient means of delivery in order to yield necessary expression of the desired antigens, resulting immunogenic response and ultimately the success of this technique. One method for delivering nucleic acid sequences such as plasmid DNA is the electroporation (EP) technique. The technique has been used in human clinical trials to deliver anti-cancer drugs, such as bleomycin, and in many preclinical studies on a large number of animal species.
The influenza virus genome is contained on eight single (non-paired) RNA strands that code for eleven proteins (HA, NA, NP, M1, M2, NS1, NEP, PA, PB1, PB1-F2, PB2). The segmented nature of the genome allows for the exchange of entire genes between different viral strains during cellular cohabitation. The eight RNA segments are: HA, which encodes hemagglutinin (about 500 molecules of hemagglutinin are needed to make one virion); NA, which encodes neuraminidase (about 100 molecules of neuraminidase are needed to make one virion); NP, which encodes nucleoprotein; M, which encodes two matrix proteins (the M1 and the M2) by using different reading frames from the same RNA segment (about 3000 matrix protein molecules are needed to make one virion); NS, which encodes two distinct non-structural proteins (NS1 and NEP) by using different reading frames from the same RNA segment; PA, which encodes an RNA polymerase; PB1, which encodes an RNA polymerase and PB1-F2 protein (induces apoptosis) by using different reading frames from the same RNA segment; and PB2, which encodes an RNA polymerase.
Influenza hemagglutinin (HA) is expressed on the surface of influenza viral particles and is responsible for initial contact between the virus and its host cell. HA is a well-known immunogen. Influenza A strain H5N1, an avian influenza strain, particularly threatens the human population because of its HA protein (H5) which, if slightly genetically reassorted by natural mutation, has greatly increased infectivity of human cells as compared to other strains of the virus. Infection of infants and older or immunocompromised adult humans with the viral H5N1 strain is often correlated to poor clinical outcome. Therefore, protection against the H5N1 strain of influenza is a great need for the public.
There are two classes of anti-influenza agents available, inhibitors of influenza A cell entry/uncoating (such as antivirals amantadine and rimantadine) and neuraminidase inhibitors (such as antivirals oseltamivir, zanamivir). These antiviral agents inhibit the cellular release of both influenza A and B. Concerns over the use of these agents have been reported due to findings of strains of virus resistant to these agents.
Influenza vaccines are a popular seasonal vaccine and many people have experienced such vaccinations. However, the vaccinations are limited in their protective results because the vaccines are specific for certain subtypes of virus. The Centers for Disease Control and Prevention promote vaccination with a “flu shot” that is a vaccine that contains three influenza viruses (killed viruses): one A (H3N2) virus, one A (H1N1) virus, and one B virus. They also report that the viruses in the vaccine change each year based on international surveillance and scientists' estimations about which types and strains of viruses will circulate in a given year. Thus, it is apparent that vaccinations are limited to predictions of subtypes, and the availability of a specific vaccine to that subtype.
There still remains a need for effective influenza vaccines that are economical and effective across numerous subtypes. Further, there remains a need for an effective method of administering DNA vaccines to a mammal in order to provide immunization against influenza either prophylactically or therapeutically.